The present invention relates to communication systems. More particularly, and not by way of limitation, the present invention is directed to a method and arrangement for setting up Label Switched Paths (LSPs), which ensures that LSP-setup for a particular class of flows is triggered only when sufficient load is offered for that class of flows.
Multi-Protocol Label Switching (MPLS) is a well established technology that enables a network to carry traffic belonging to a single Forwarding Equivalence Class (FEC) over connection-oriented Label Switched Paths (LSPs). Current implementations of MPLS architectures trigger LSP-setup either by explicit user configuration, by routing updates, or by signaling of a client across an MPLS User-to-Network Interface (UNI).
LSP-setup by explicit user configuration is achieved by the user explicitly configuring LSPs. LSP tunnels may be set up by signaling protocols such as Resource Reservation Protocol Traffic Extension (RSVP-TE) or Constrained based Label Distribution Protocol (CR-LDP). LSP tunnels are described in “Requirements for Traffic Engineering Over MPLS,” D. Awduche, et. al., RFC 2702, IETF Network Working Group, September 1999. The RSVP-TE protocol is described in “RSVP-TE: Extensions to RSVP for LSP Tunnels,” D. Awduche et. al. RFC 3209, IETF Network Working Group, December 2001. The CR-LDP protocol is described in “Constrained based LSP Setup using LDP,” B. Jamoussi et. al., RFC 3212, IETF Network Working Group, January 2002. These three documents are hereby incorporated herein by reference.
A disadvantage of LSP-setup by explicit user configuration is that this approach is not very scalable. Although it is possible to map multiple traffic flows into the same LSP tunnel by mapping multiple FEC entries at the Ingress Label Edge Router (Ingress-LER) to the same Next-Hop Label Forwarding Entries (NHLFE), this needs to be explicitly configured. Also, this approach does not adapt well to changing network conditions and topologies. The approach also tends to tie up network resources on a more permanent basis or till the user un-configures the LSP.
LSP-setup by routing updates occurs when the service provider implementing an MPLS core allows triggering of an LSP-setup based on prefix advertisements of dynamic routing protocols such as Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP). All traffic to these destination prefixes are carried by the LSPs that are set up.
A disadvantage of LSP-setup by routing updates occurs because the LSP-setup for each prefix carries all types of traffic to that destination. Since this mechanism is dependent on control information such as routing updates, the LSPs remain underutilized in the absence of traffic.
LSP-setup by signaling across an MPLS UNI can be triggered by client applications signaling across an MPLS UNI interface across a link between Customer Equipment and Provider Equipment boxes (i.e., a CE-PE link).
A disadvantage of LSP-setup by signaling across an MPLS UNI is that this approach is limited to applications where service providers set up LSPs to connect Customer Equipment (CE) boxes at different sites across their MPLS-capable network. Thus, the approach mandates a point of operation and is not generally applicable.
The current art needs an improved method and arrangement for setting up LSPs that overcomes the disadvantages of the prior art. The present invention provides such a method and arrangement.